So I am absolutely astounded at how little is actually discussed about alpha channels and such, in the post production industry. It seems to be a deep abyss of information, or vice-versa, the information keeps falling into an abyss. Being in the stock footage biz, I always get really ticked off at some of the houses that can't accept a full 32 bit depth video file. We know these files as pre-keyed, alpha-keyed, masked, whatever the heck you want to call them. They show up in the Quicktime (.mov) world as files that were created in progressive mode a la rendering using the png or animation codec portions. But the funny thing is, many forget to turn on the damn "RGB plus Alpha" when doing this. It's like who is this guy Alpha anyway? And why is no longer in Beta? Yes, that was "punny". I know.
So let's first start with this guy named "Alpha". After all he is the invisible or transparent brother of Red, Green and Blue. (Okay, Photoshop guys, this also can apply to you.) But before we go there, let's get to brass tacks about computer stuff. Stuff such as bytes. Hungry? If you remember (and this applies only to people that are younger than 50 and/or worked at a company like IBM), a byte consists of 8 bits. Hence, 8 bits equals a byte, 2 bytes equals too much food, and 4 bytes equals the full depth of an RGBA rendered file. Hence, red (8 bits), green (8 bits), blue (8 bits) and Alpha (8 bits) - darn, there is that Alpha dude again. But, really, this is called a 32 bit depth file. As in 4 x 8 = 32!
So how come 8 bits for Alpha? Well, you see, back in the day, 2 bits equaled a quarter, hence 8 bits was a buck. Confused? You should be. This has absolutely nothing to do with anything about Alpha channel. But think about it. If you only got 3/4 of a buck (a.k.a. 6 bits), you can't even get something off of the Dollar Menu at Micky D's. So perhaps that last quarter may mean something yet. In video terms it means a heck of a lot!
Back to the 8 bit thing. Eight (8) bits basically gives, in computer terms, 256 variations of something. (a.k.a. 0-255) Could it be brightness? Could it be transparency? Could it be a shade value? Perhaps it delivers a bit of all of these. But that doesn't matter for this topic right now. The key is that there are 4 of these 0-255's if you include an alpha channel. So what the heck for, this alpha thingy? It's transparent! You can't even see it! So why even worry about it? Well, you can't see the air either and yet you need it to live. Don't you? Video files can do amazing things if they are beyond the typical 24 bits (3/4's remember? or instead of 32 bits). For one, they can grow really nicely into fat plump and juicy files. Yes, they are bit bigger than your standard 24 bit depth file. But they are well worth it.
Here for example is a standard 24 bit file:
Notice how the penny covers the silver dollar? Actually it is a video layer track that gets re-sized as the clip plays. The silver dollar appears only a "bit", pardon the pun. Looks pretty useless. Or I suppose one could say this is the value of our assets now.... you know... "penny on the dollar". Okay, so shoot me. :)
Here is the same thing, but with 32 bits, and, yes, you guessed right, an Alpha channel:
This is actually the exact same clip as the one before, but with the Alpha channel fully activated. So much nicer. And notice how the dollar seems to grow. Wishful thinking I suppose.
The final message here? The government will spend a dollar to save a penny? No. But more importantly, 8 bits needs to be seen (or not seen - i.e. transparent), to show 8 bits more clearly. Get it?
All right then. Now that you see the concept, stay tuned for mere detail in future blog entries right here! I will cover this topic in great detail as it is one of the more important topics to understand if you are going to be doing some cool video work. Aside from that, having this knowledge could actually yield you several 8 bits in your wallet. Stay tuned.